Lesson 39 Introducing the 4046 Voltage-Controlled Oscillator

Chapter Lesson 39 Introducing the 4046 Voltage-Controlled Oscillator

Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects
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Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects

  • This is the switch that you will use for the largersystem. But first, do some initial voltage testing atthe output. Check for a few critical items.1.What is the peak voltage?2.How long does it take to drain to 0 volts?3.How sensitive is it?a. Is any voltage fed through if you touchacross the bottom of the push button?b. Substitute an LDR into the spot for thepush button. Anything?4.Change the values for R1 and C1. Does theRC act the way you would expect?5.Take the zener diode out. Replace it with awire. Do the measurements again. What is thebiggest effect that the zener has on this switch?Lesson 39Introducing the 4046Voltage-Controlled OscillatorThe 4046 chip takes the analog voltage from theRC switch and changes it directly into digital“clock” signals (Table L39-1). It is the “analog-to-digital” converter. How does it count? Digitally! 0 – 1 – 0 – 1 – 0 – 1 – 0The voltage input at pin 9 determines thefrequency output at pin 4. Breadboard this circuit(see the following Parts Bin).Pay attention to the schematic in Figure L39-1.Only three pins are connected on the top side ofthe IC. Don’t accidentally build on top of the 4046.Lesson 39 ■Introducing the 4046 Voltage-Controlled Oscillator 153Figure L38-6Input Pin 9 from RC1Processor VCOOutput Rolldown Clock SignalThe rate of voltage drain is The VCO in the 4046 comparesThe length of the rolldown is controlled by the value of the input voltage at pin 9 to controlled by RC1.R1 and C1 (RC1).the supply voltage at pin 16.The voltage from RC1 is There is a direct relation The output starts quickly but moving from about 4 volts between the input voltage and “rolls down” to a complete stop.to ground.the speed of oscillation at pin 4, the output.The higher the input voltage, the Definition: A clock signal is a rise faster the oscillation output. from 0 V to V+ in less than 5 S The maximum oscillation is (1 = 1 micro = 0.000001).controlled by R2 and C2 (RC2).TABLE L39-1System Diagram of Our Application of the 4046 IC